在Edit上使用MVC的Entity Framework 4.3不保存复杂对象

Question

我用Northwind数据库做了一个小项目来说明问题所在.

这是控制器的动作:

[HttpPost]
public ActionResult Edit(Product productFromForm)
{
    try
    {
        context.Products.Attach(productFromForm);
        var fromBD = context.Categories.Find(productFromForm.Category.CategoryID);
        productFromForm.Category = fromBD;
        context.Entry(productFromForm).State = EntityState.Modified;
        context.SaveChanges();
        return RedirectToAction("Index");
    }
    catch
    {
        return View();
    }
}

context在Controller的构造函数中实例化new DatabaseContext().

public class DatabaseContext:DbContext
{
    public DatabaseContext()
        : base("ApplicationServices") {
        base.Configuration.ProxyCreationEnabled = false;
        base.Configuration.LazyLoadingEnabled = false;
    }

    public DbSet<Product> Products { get; set; }
    public DbSet<Category> Categories { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder){

        modelBuilder.Configurations.Add(new ProductConfiguration());
        modelBuilder.Configurations.Add(new CategoriesConfiguration());
    }

    private class ProductConfiguration : EntityTypeConfiguration<Product> {
        public ProductConfiguration() {
            ToTable("Products");
            HasKey(p => p.ProductID);
            HasOptional(p => p.Category).WithMany(x=>x.Products).Map(c => c.MapKey("CategoryID"));
            Property(p => p.UnitPrice).HasColumnType("Money");
        }
    }

    private class CategoriesConfiguration : EntityTypeConfiguration<Category> {
        public CategoriesConfiguration() {
            ToTable("Categories");
            HasKey(p => p.CategoryID);
        }
    }
}

public class Category {
    public int CategoryID { get; set; }
    public string CategoryName { get; set; }
    public string Description { get; set; }
    public virtual ICollection<Product> Products { get; set; }
}

public class Product {
    public int ProductID { get; set; }
    public string ProductName { get; set; }
    public string QuantityPerUnit { get; set; }
    public decimal UnitPrice { get; set; }
    public Int16 UnitsInStock { get; set; }
    public Int16 UnitsOnOrder { get; set; }
    public Int16 ReorderLevel { get; set; }
    public bool Discontinued { get; set; }
    public virtual Category Category { get; set; }
}

问题是我可以保存产品中的任何内容,但不能保存类别的更改.

对象productFromForm在productFromForm.Product.ProductID中包含新的CategoryID而没有问题.但是,当我Find()从上下文中检索对象的类别时,我有一个没有Name和Description的对象(都保持为NULL)并且SaveChanges()即使ID已经为属性更改,也不会修改引用Category.

知道为什么吗？

Answer 1

您(显然)改变的关系不会得到保存,因为您没有真正改变关系:

context.Products.Attach(productFromForm);

该行将productFromFormAND 附加productFromForm.Category到上下文中.

var fromBD = context.Categories.Find(productFromForm.Category.CategoryID);

该行返回附加的对象productFromForm.Category,而不是数据库中的对象.

productFromForm.Category = fromBD;

该行分配相同的对象,因此它什么都不做.

context.Entry(productFromForm).State = EntityState.Modified;

此行仅影响标量属性productFromForm,而不影响任何导航属性.

更好的方法是:

// Get original product from DB including category
var fromBD = context.Products
    .Include(p => p.Category)  // necessary because you don't have a FK property
    .Single(p => p.ProductId == productFromForm.ProductId);

// Update scalar properties of product
context.Entry(fromBD).CurrentValues.SetValues(productFromForm);

// Update the Category reference if the CategoryID has been changed in the from
if (productFromForm.Category.CategoryID != fromBD.Category.CategoryID)
{
    context.Categories.Attach(productFromForm.Category);
    fromBD.Category = productFromForm.Category;
}

context.SaveChanges();

如果在模型中将外键作为属性公开,则会变得容易得多 - 正如@Laniency的答案和前一个问题的答案中所述.使用FK属性(并假设您Product.CategoryID直接绑定到视图而不是Product.Category.CategoryID),上面的代码简化为:

var fromBD = context.Products
    .Single(p => p.ProductId == productFromForm.ProductId);
context.Entry(fromBD).CurrentValues.SetValues(productFromForm);
context.SaveChanges();

或者,您可以设置可以Modified使用FK属性的状态:

context.Entry(productFromForm).State = EntityState.Modified;
context.SaveChanges();